Olefin resins are molded by various molding methods and used in a variety of applications. Properties required for the olefin resins vary depending on the molding methods or applications.
Of the olefin resins, ethylene/α-olefin copolymers such as ethylene/propylene copolymer, ethylene/butene copolymer, and ethylene/octene copolymer are widely used in automobile parts such as bumpers and instrument panels, packaging materials (such as low temperature heat sealable films and easy peel films), sporting goods (such as midsoles in sports shoes), and wire coverings, because of their excellent properties, such as being lightweight, having a low specific gravity, flexibility, low melting point, and excellent compatibility with other olefin resins, and being easily recyclable. At the same time, improvements have been demanded, because of the problems that ethylene/α-olefin copolymers have a poor heat resistance due to being non-crystalline or low-crystalline polymers, and that the resulting molded articles may be sticky depending on the proportion of ethylene structural units.
In order to solve the above mentioned problems, studies have been reported in which an effort is made to arrange a crystalline segment and a non-crystalline or low-crystalline segment in blocks during the polymerization stage in the production of an olefin copolymer. Patent Document 1 discloses a technique to produce an olefin block copolymer in which a crystalline ethylene homopolymer segment and an ethylene copolymer segment are arranged on a straight-chain using a specific living polymerization catalyst. Further, Patent Document 2 discloses that an olefin block copolymer having a multi-block structure can be obtained by using two different types of transition metal complex catalysts varying in copolymerizability, and by adding a zinc compound to allow a reversible chain transfer reaction to occur through the zinc compound.
The copolymers disclosed in these documents are proposed for the purpose of improving the heat resistance by incorporating a crystalline segment into the polymer. However, the copolymer disclosed in Patent Document 2, in particular, is associated with other problems that the zinc compound used as a chain transfer agent remains in the finally resulting polymer component, and that the improvement in reducing the stickiness is limited because of the formation of a copolymerization component which remained unincorporated into the block structure. Further, in the copolymers obtained by the methods disclosed in the above mentioned Patent Document 1 and Patent Document 2, the number of free terminals of the crystalline segment per one molecule is limited to 2 or less, in principle, and accordingly, the size of spherulites formed during the crystallization process cannot be controlled, possibly leading to a deterioration of mechanical performance and optical properties.